1. Field of the Invention
This invention relates to a heat developable light-sensitive material, and more specifically, to an improved heat developable light-sensitive material using a novel toning agent and capable of providing a black image.
2. Description of the Prior Art
Photographic processes using silver halide have been most widely used heretofore because of their superiority in photographic characteristics such as sensitivity or gradient to the characteristics of electrophotographic or diazo photographic processes. Silver halide photographic materials are processed with a liquid developer, and then subjected to various treatments using liquids such as stopping, fixation, rinsing or stabilization in order to stabilize the undeveloped background. Accordingly, these processing steps require time and labor, and there is a risk to the working personnel due to the handling of chemicals. These chemicals also cause contamination of the processing room and the hands or clothes of the worker.
In order to remove the above defects of silver halide photographic processes, various attempts have been made to use a heat developable photographic process which does not employ treatment with chemical solutions in which a heat developable light-sensitive material is exposed, and the resulting latent image is developed by heating the light-sensitive element and, at the same time, stabilized.
Various types of heat developable light-sensitive materials are known. For example, U.S. Pat. Nos. 3,394,393, 3,394,394, and 3,391,395 disclose methods in which a combination of a lower haloalkane as a photoactivator and a furfurylidene compound as a dye-forming agent is exposed, and then heated for development.
Other dry developing methods using heat and light-sensitive elements therefore are disclosed in Japanese Patent Publication No. 2096/63 and U.S. Pat. Nos. 3,152,904, 3,457,075 and 3,635,719. These processes rely on using a heat developable light-sensitive material comprising a silver salt oxidizing agent such as a long-chain aliphatic carboxylic acid silver salt, silver saccharin or silver benzotriazole, a suitable reducing agent, and a light-sensitive catalyst, such as a silver halide, for this oxidizing agent-reducing agent combination.
Of the two approaches discribed above, the present invention belongs to the latter approach.
Heat developable light-sensitive materials using silver salt oxidizing agents, in most cases, provide only yellowish brown images, but it is known that they can be improved to give images of a black tone by adding a toning agent. Examples of toning agents are phthalazinone, and 2-pyrazolin-5-one, quinazoline and cyclic imides disclosed in U.S. Pat. No. 3,846,136.
However, toning agents which have been proposed so far have various defects. For example, they do not provide a pure black tone, and in particular, light-sensitive materials which have been stored in the original form for prolonged periods of time undergo deterioration in tone with the result that the tone becomes brownish. Alternatively, the toning agent volatilizes from the light-sensitive material at the time of development by heating and contaminates the developer machine used.